Is the light red or orange? If it's red don't drive it, Have it towed to get it serviced. I had a 2002 4.6 and mine came on at 40K, it was orange. Mine had to do with the a part that failed for the emissions. I did get a letter from Ford sometime before it failing that said they were extending the warranty on that part for an addtional 1 year or 12K miles. Funny why they didn't just recall it and replace it before it failed I guess they didn't want to if they didn't have to.

Do you have a AutoZone near you? They can scan your OBII port and give you the codes to help see what's wrong.

My 98 Ranger had the "Engine light " come on at about 85K, the same time my truck wouldn't start , called Ford they towed it said it was the "MAS" after the changed it , I drove it about 2 days the light came back. I took it to Auto Zone the code said it was the oxygen sensor, I changed it out, we changed all the plugs etc... and the "Light would come on and go off" when ever it felt like it I guess.
No matter what I did it would come on . It would take about 20 miles or so to come on but then I would be driving and it would go out not come on.
Finally I just "Gave-up" drove another 70K like that. I would dis connect the Battery to clear it if I felt like it. My Dads F-150 4x4 6cyl. does the same thing.
Plus I've heard it from several others even Explore owners, even the Mech. at Ford told me "Really don't worry about it if the truck is running fine" its just "One of those "Things".

Now does it go "Off" sometimes while driving? or not come on during Cold Weather?